﻿PLATE XIII. 



UPPER SILURIAN CRUSTACEA. 



Order — Merostomata. 



Sub-Order — Eurypterida. 



Pterggotus bilobus, var. y, perornatus. 



Fig. 



1 a. An almost entire example, reduced to one half the natural size. 



a, a. The antennae, detached and displaced (the points of attachment to the 



head are marked by stars). 

 o, o. The eyes ; and (le) the larval eye-spots or ocelli. 

 e. An endognath and part of another, displaced. 

 ec. The ectognaths, or swimming-feet; their great basal joints (c, c) are 



detached, and lie in front of the head. 

 m. The metastoma or post-oral plate. 

 The telson (20) is restored. 



1 b. The larval eyes, magnified three times. 



1 c. One of the large compound eyes, magnified three times. 



1 d. A portion of same, magnified fifteen times. 



1 e. The metastoma, of the natural size. 



1 /. The coxal joint of one of the ectognaths, natural size. 



1 g. Part of a thoracic segment, magnified three times, to show the scale-like markings on 



its upper part. 

 1 Ji. Three of the branchise, magnified three times, seen in this specimen where a portion 



of a thoracic segment has been removed. 



Erom the Uppermost Silurian of Lesmahago, Lanarkshire. 



Drawn from a specimen in the Museum of Practical Geology, Jermyn Street. 



